Our web site is at http://people.ouc.bc.ca/pshipley/aikido
. We don't have any problems at all with students, and our school is a fraction of your size (only around 5000 students). I think you'll find that there will be plenty of interest. Since your overhead will be practically nonexistent (most schools will give you free mat/gym time if you are a student club) the students can pretty easily afford the dues that you'll charge for broken weapons, etc.
Feel free to send me an email if I can help answer any specific questions,
P.S. 400,000 students? holy cow...